Re: 1975 johnson 50
you might find one on ebay. or these. you are still going to need the controls, as i don't think it will convert.
Salvage yards.
sea-way.com
outboard-parts.com
laingsoutboards.com
tcoutboard.com
fairwindsmarina.com
salvagemarine.com
marinepartsoutlet.com
Superior Marine (800-338-9281)